Phase-locked loop is very common in telecommunication, control, and other electronic application. PLL can be used to demodulate FM signal, produce a stable clock signal, or to recover a synchronization signal from noise. Many single chip integrated circuits (IC) are produced for this PLL system, and LM359 is one of them. This PLL is capable to operate up to 5MHz, flexible for many applications.

LM359 Voltage Controlled Oscillator circuit schematic

Phase-locked loop or PLL is a kind of control system that produce an oscillation whose phase is synchronized with the input’s phase. In PLL system, the input signal is often called a reference signal. The construction of a PLL system consist of a phase difference detection and a voltage controlled oscillator (VCO). The phase difference detector accept inputs from the reference signal and the VCO’s output. If there’s a mismatch between the VCO output and the reference’s phase then the phase difference detector will produce a compensation voltage that is fed to the VCO to correct this error. [Circuit’s schematic diagram source: National Semiconductor Datasheet]